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University of Maryland - University College
What is energy? What is work? List some examples of each.
If the internal energy of the products of a reaction is higher than the internal energy of the reactants, what is the sign of E for the reaction? In which direction does energy flow?
What is a buffer? How does a buffer work? How does it neutralize added acid? Added base?
If energy flows out of a chemical system and into the surroundings, what is the sign of Esystem?
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So now that we've talked more about gasses and liquids, let's actually talk about solids. So solids come in two broad categories, and so we can talk about solids as crystalline solids. And so when we talk about something that is crystalline, we think about something that is ordered. And so we'll talk more about what that means when we bring up lattice and basis. But I also wanted to point out that there is also another type of solid called a more festival. It's and so amorphous solids can be thought of as the opposite of crystalline solids so thes are not ordered and random on DSO. These do not form crystals like the crystalline solids, and so crystalline solids are ordered in lattices. And so lettuces are systems that specify where the atom or molecule or on is located in a material. And so we can say that for any given material we can represent thes by these points or dots. And so we can say that this can be some kind of generic lattice for some kind of crystalline solid, And what's important to know is that you can also identify a basis for each last point and so a basis is something that gives us more information about what is located on the last point. And so, for example, you can have again some kind of molecule on the let US point as well as some Adam or some island. And so we'll talk more about this when we actually talked about the different type of crystalline solids. And so there are actually a lot of different kind of places, um, that we will observe for different solids. But essentially there are common lattices across all materials on DSO. Those can be represented by unit cells, which we'll talk about more later. But essentially there are 14 kinds of robbing classes. Uh, there are seven different unit cells that you can possibly have for many materials, and so each unit self is unique in terms of the spacing in three dimensional space with the different last points, and so we'll learn more about that later. But essentially we can talk about a broad array of different materials based on the spacing between each of the last point, and so under crystalline solids. There are three different types of assault, and so the first one is an Ionic solid, and we've seen this a lot before when we talked about a lot of ionic compounds. And so these include things like sodium chloride, which has a rock salt structure as well as season chloride, which is essentially a simple cubic structure with a body center point. And so we will talk more about the different structures later. Um, but this is one example of an Alec solid, and we also have a zinc blunt, which we won't talk about more. Um, but this is also technically antibiotic solid, and so you can actually see that I don't like. Solids are essentially these ionic compounds, and the reason why they make these ionic solids is because of the electrostatic interactions between the islands and so these interactions are very strong. And so Ionic solids tend to have very high melting points, Uh, and so we can recognize an ionic solid by the fact that you have ionic bonding. And when you look at ionic solids in terms of how old's like in a lot of for its bases, it is simply just the molecular formula. And so, if we were to actually draw some kind of generic lettuce has shown here Basically, for each of these points, this would simply be a sodium about it Teoh, a chlorine atom. And so we can imagine that at each one is point, we have, um the small you on each of these points and so this would be the basis for some kind of generic less. And another type of crystalline salt that we can have is called a molecular solid. And so we've seen molecular assaults before on DSO. These include things like sulfur, which has formula of s eight as well as water but in a nice form as well as carbon dioxide but in the form as dry ice. And so I'm like they're solids, as you can see are made up of molecules. And so the basis is Alka. Suit is also technically the molecular formula. But for the next solid, this is the island compound. And for molecular solids, thes are molecules that are mainly bonded by covalin bonding. And so we can also specify that s so let's have ionic bonding and electrostatic forces. And again, thes tend to have my multi points. And molecular solids tend to have low melting points Just because the bonds are not as strong compared thio those of the ionic solid and so began for the basis we would have the molecule and so we can imagine that reach basis. For example, in ice, each of the latest points are simply a water molecule firm. And so these are pretty easy to recognize, mainly because we have a villa bonding. And so the electron activities between the atoms are quite small. Um, or at least in the case of H two, is technically, um, large. But in comparison to the solid, not so much. And so that is another type of crystalline solid. And so the last one that we'll talk about is actually the atomic solids, then sue. These are basically made of atoms, and so we can think of carbon, but in the form of graphite and diamond as well as boron and onto her medals like iron. And so, for a talk solid, these air only made up of atoms. But these can have pretty strong forces as well. And so for medals they have a special kind of bonding. And as for carbon, we see a lot of network of violent bonding on DSO UM atomic solids are simply made up of the atom and can be also very strong materials as well. I'm just going back to the Christmas holiday. Morpheus solids again. We have two different types where amorphous is not ordered and Christian souls are ordered into a lot of points. And so these are the different types of crystalline solids, and they again are crystalline solids because they have defined lettuce points, Um, at which there are different species as well, and for amorphous solids. Again, they do not have a lot of and are not order. And so with that, let's actually go into a couple of examples to better understand the differences between three different types of crystalline solids, as well as understanding the lettuce and the basis. So for the first of all, what's actually determined the lot of points of some kind of solid as well as the basis. And so let's say we have some January crystal that looks like so and so when we're talking about lattices Dan bases in this case, we don't really need to understand what exactly it is. But it's more important to understand the structure of the material and how it repeats in space. And so let's say we again have some kind material that has the student control structure, and so you want to determine the lattice as well as basis. And so before we said that lettuces are basically points that represent where each of the BCS are in space and so we can see that we basically have a repeat unit of the shape. And so we know that this repeats itself four times across the road and another set on the second row. And so we can say that theologies looks like this where each of these repeating units can be represented as thes dots and the way that it is structured shows that we have the four dots running across one row and another set on the second round. And so again, this is the latest, because this is a simple fly structure off the material where each of the points represent a repeating unit. And since we know that the shape is the repeating unit, we know that this must be the basis because this is the simplest repeating unit that we see in our material. And so this is generally how you would identify the lettuce and the basis for some kind of material. And so, for our next problem, let's actually do the same thing. And let's actually look at some kind of cute. And so let's say that we have some kind of material in three D space that looks like this. And so the Cube actually will just give us more of a structure as to what this looks like. But let's say that we have some kind of three dimensional structure that looks like this, and we also want to figure out the lettuce as well as the basis. And so for this problem, we see that we can identify the basis pretty easily because even though we have thes shapes at these quarters, we know that if we extend the structure, we know that it will extend and have this little dot running across this direction as well. And so we can say that basis looks like this because this is the simple repeating unit across the Cube and three dimensional space. And as for the latest, we know that we can reduce this basis into a single point. And so if we draw a small cube to mimic the structure. We know that we have a last point at each of the corners of the Cube, and we also know that we have another last point right in the center for this basis. And so we can draw one right here, too. And so these would be a lot of points for our structure. And later we'll learn that this is a B, C, C or body center cubic structure on DSO. We can see that by looking at some kind of material, we can deduce what the latest would be like as well as the basis, Um, just by observing it and seeing what is the simplest repeating unit across the material. And so this is very useful in terms of identifying the different structures of material because there is such a diverse array of different types of structures that you can have. And so this is a very useful tool to classify solids. And for our last example, let's actually identify some solids. And so let's say we want to figure out what Well, boron is magnesium oxide, ammonium chloride and, well, my two and so again, going back to our definitions, we know that there are three different types of crystalline solids, so we can have an ionic solid, a molecular solid or an atomic solid. And so, just by looking at this list, we know that we have an atomic solid for B because this is only made up of one type of Adam and specifically the Adam must be the basis. And so the last points on Lee have atoms on it, and so that is characteristic of the atomic solid. And as for my knees and oxide, you know that this must be an ionic solids because we observe ionic bonding between the M, G and O. And so this must be an ionic solid. And the same can be said for the ammonium chloride Onley because even though it does have the NH four in it, this is overall and ionic solid because the NH four will donate its electron toothy chlorine and thus we have a chloride and an ammonium ion. And so this is an ionic solids. And as for the last one, we know that this is a molecular solid because it is different in the case of the boron, because the born can simply have a structure, um, with Adams as its basis. But since I too, is basis, we know that I, too, has equal a bond between each other. And so this must be a molecular solid.
Acids and Bases